Learn Hardcore Greek: Για εμάς αυτή η εξέταση είναι μεγάλη επιτυχία, γιατί πριν έναν χρόνο είχαμε αποτυχία στο ίδιο μάθημα. - For us this exam is a big success, because a year ago we had a failure in the same subject.

για is a preposition that often corresponds to English for, about, or as far as … is concerned.
Here, Για εμάς means from our point of view / as far as we are concerned.

So Για εμάς αυτή η εξέταση είναι μεγάλη επιτυχία =
For us, this exam is a great success / As far as we’re concerned, this exam is a great success.

Why is it εμάς and not μας in Για εμάς?

Greek personal pronouns have a stressed (strong) form and an unstressed (clitic) form.

εμείς / εμάς = stressed forms (we / us)
μας = unstressed form (us / our)

After prepositions like για, σε, με, Greek normally uses the stressed form:

για εμάς – for us
σε εμάς – to us
με εμάς – with us

In everyday speech, you will also hear and see για μας, but this is really just a reduced pronunciation of εμάς; grammatically it is still the stressed form in that position. The fully unstressed μας appears mainly around the verb:

Μας είπε την αλήθεια. – He told us the truth.

Why is the order αυτή η εξέταση and not η εξέταση αυτή? Are both correct?

Both αυτή η εξέταση and η εξέταση αυτή are grammatically correct.

αυτή η εξέταση = this exam (demonstrative before the article+noun)
η εξέταση αυτή = also this exam (demonstrative after the noun)

They are very close in meaning. Rough tendencies:

αυτή η εξέταση is very common and neutral.
η εξέταση αυτή can sound a bit more emphatic or contrastive, like this exam (as opposed to other exams).

In this sentence, αυτή η εξέταση is perfectly natural and probably the most common way to say this exam in modern Greek.

Why is it μεγάλη επιτυχία and not something else? What is agreeing with what?

επιτυχία (success) is a feminine noun in Greek, nominative singular here.

Adjectives must agree with the noun in gender, number, and case, so:

feminine, singular, nominative: μεγάλη επιτυχία (big/great success)
masculine, singular, nominative would be: μεγάλος μαθητής (big / great student – masculine)
neuter, singular, nominative: μεγάλο πρόβλημα (big problem – neuter)

So we need μεγάλη (feminine) to match επιτυχία (feminine), giving μεγάλη επιτυχία.

Why is the verb είναι (is) used and not ήταν (was)? The exam is in the past, right?

Yes, the exam itself took place in the past, but είναι focuses on the current result or status:

Για εμάς αυτή η εξέταση είναι μεγάλη επιτυχία
= For us, this exam is a big success (for us now; that’s how we see it).

If you say:

Για εμάς αυτή η εξέταση ήταν μεγάλη επιτυχία,

you are reporting it more as a past fact, something that was a success at that time.

Both are correct; the choice is about nuance:

είναι – the success is felt as a present, continuing reality.
ήταν – the speaker is placing the success more clearly in the past.

What is going on with πριν έναν χρόνο? Why is έναν χρόνο in that form, and could it be different?

πριν is a preposition meaning before; in time expressions it functions much like English ago, and it takes the accusative case.

πριν έναν χρόνο = one year ago / a year ago
- έναν is the masculine accusative form of ένας (one).
- χρόνο is the accusative of χρόνος (year).

Variations you may hear:

πριν ένα χρόνο – very common; the final -ν is dropped in everyday speech.
πριν από έναν χρόνο – also common; από adds no real extra meaning here.

So all of these are natural:

πριν έναν χρόνο
πριν ένα χρόνο
πριν από έναν χρόνο

They all mean a year ago.

Do we need από after πριν, as in πριν από έναν χρόνο? What is the difference?

No, από is not required in time expressions with πριν.

πριν έναν χρόνο – a year ago
πριν από έναν χρόνο – also a year ago

Differences:

In time expressions, they are effectively the same in meaning.
πριν από is slightly more explicit or slightly more colloquial, depending on context, but both are very standard.
When πριν is followed by a clause, you normally use only πριν:
- πριν φύγουμε – before we leave
- πριν να φύγουμε is also heard, but πριν φύγουμε is more standard.

In this sentence, πριν έναν χρόνο is perfectly correct and natural.

Why does the sentence say είχαμε αποτυχία instead of using a verb like αποτύχαμε?

Greek has both:

a noun: αποτυχία – failure
a verb: αποτυχαίνω (aorist: απέτυχα, 1st plural: αποτύχαμε) – to fail

είχαμε αποτυχία literally means we had a failure. It is a light-verb construction (verb έχω + noun) that focuses on the event/result:

πριν έναν χρόνο είχαμε αποτυχία στο ίδιο μάθημα
≈ a year ago we had a failure in the same course / we failed in the same course.

You could also say:

πριν έναν χρόνο αποτύχαμε στο ίδιο μάθημα – a year ago we failed the same course.

Both are grammatical and natural. Small nuances:

είχαμε αποτυχία often sounds a bit more like we had a failure (as an outcome).
αποτύχαμε is a straightforward verbal we failed.

Also, note that είχαμε αποτυχία is just simple past of έχω + noun. It is not a past perfect like English we had failed. The closer Greek past perfect would be:

είχαμε αποτύχει στο ίδιο μάθημα – we had failed the same course.

What is the difference between γιατί and επειδή for “because”? Could we use επειδή here?

Yes, you could say:

… είναι μεγάλη επιτυχία, επειδή πριν έναν χρόνο είχαμε αποτυχία στο ίδιο μάθημα.

In this sentence, γιατί and επειδή are interchangeable and both mean because.

General points:

γιατί can mean both why (in questions) and because (in answers/clauses):
- Γιατί έφυγες; – Why did you leave?
- Έφυγα γιατί ήμουν κουρασμένος. – I left because I was tired.
επειδή only means because (never “why”), and it often sounds a bit more formal or explicitly causal, but in everyday speech people use γιατί a lot for because.

In this sentence, γιατί is very natural and idiomatic.

What does στο ίδιο μάθημα mean exactly, and why is it στο?

στο ίδιο μάθημα means in the same subject / in the same course / in the same class.

σε = in, at, to (a very common preposition)
το = the (neuter, singular, accusative)
In standard Greek, σε + το contract to στο:
- σε + το μάθημα → στο μάθημα

Other similar contractions:

σε + τον → στον (e.g. στον φίλο)
σε + την → στη(ν) (e.g. στη δουλειά)
σε + τα → στα (e.g. στα παιδιά)

So στο ίδιο μάθημα literally is in the same lesson/subject/course.

What does μάθημα mean here? Is it “lesson”, “class”, or “subject”?

μάθημα is a flexible word; depending on context it can mean:

A single lesson or class session
- Έχουμε μάθημα στις 9. – We have class at 9.
A school subject
- Το αγαπημένο μου μάθημα είναι τα Μαθηματικά. – My favourite subject is Math.
A university course / module
- Πέρασα το μάθημα της Φυσικής. – I passed the Physics course.
Figuratively, a (life) lesson
- Αυτό ήταν μεγάλο μάθημα για μένα. – That was a big lesson for me.

In είχαμε αποτυχία στο ίδιο μάθημα, given that we are talking about an exam (εξέταση), μάθημα here most naturally means course / subject (the course in which the exam takes place).